This invention relates to control of actuating fluid for use in an intensified fuel injection system for internal combustion engines. More particularly, the present invention controls a variable output pump that provides pressurized actuating fluid to an accumulator.
A prior art hydraulically actuated, intensified injection system (commonly a HEUI injection system) 10 is depicted in prior art FIG. 1 and consists of five major components:
Electronic Control Module (ECM) 20
Injector Drive Module (IDM) 30
High Pressure actuating fluid supply pump 40
Rail Pressure Control Valve (RPCV) 50
HEUI Injectors 60
Electronic Control Module (ECM) 20
The ECM 20 is a microprocessor which monitors various sensors 22 from the vehicle and engine as it controls the operation of the entire fuel system 10. Because the ECM 20 has many more operational inputs than a mechanical governor, it can determine optimum fuel rate and injection timing for almost any condition. Electronic controls such as this are absolutely essential in meeting standards of exhaust emissions and noise.
Injector Drive Module (IDM) 30
The IDM 30 is communicatively coupled to the ECM 20 and receives commands therefrom. The IDM 30 sends a precisely controlled current pulse to energize the solenoid of each injector. Such energization acts to port high pressure actuating fluid to the intensifier of the respective injector 60. The timing and duration of the IDM 30 pulse are controlled by the ECM 20. In essence, the IDM 30 acts like a relay.
High Pressure Actuating Fluid Supply Pump 40
The high pressure actuating fluid supply pump 40 is a single stage pump and is in the prior art typically a seven piston fixed displacement axial piston pump and is driven by the engine. The high pressure actuating fluid supply pump 40 draws in low pressure actuating fluid (most commonly engine oil, but other actuating fluids could be used as well) from the reservoir 46, elevates the pressure of the actuating fluid for pressurization of the accumulator or rail 42. The rail 42 is plumbed to each injector 60. During normal engine operation, pump output pressure of the high pressure actuating fluid supply pump 40 is controlled by the Rail Pressure Control Valve (RPCV) 50, which dumps excess flow back to the return circuit 44 to the reservoir 46. The reservoir 46 is at substantially ambient pressure and may be at the normal pressure of the lubricating oil circulating in the engine of about 50 psi. Pressures for specific engine conditions are determined by the ECM 20.
Rail Pressure Control Valve (RPCV) 50
The RPCV 50 is an electrically operated dump valve, which closely controls pump output pressure of the high pressure actuating fluid supply pump 40 by dumping excess flow to the return circuit 44 and to the reservoir 46. A variable signal current from the ECM 20 to the RPCV 50 determines pump output pressure. Pump pressure can be maintained anywhere between about 450 psi and 4000 psi during normal engine operation. When the actuating fluid is engine lubricating oil, pressure while cranking a cold engine (below 50 degrees F.) is slightly higher because cold oil is thicker and components in the respective injectors 60 move slower. The higher pressure helps the injector 60 to fire faster until the viscosity of the actuating fluid (oil) is reduced.
HEUI Injector 60
Injectors 60 of this type are known and are representatively described in U.S. Pat. Nos. 5,460,329 and 5,682,858, incorporated herein by reference. The injector 60 includes an intensifier piston and plunger, the actuating fluid acting on the intensifier to pressurize a volume of fuel acted upon by the plunger. The injector 60 uses the hydraulic energy of the pressurized actuating fluid (preferably, lubricating oil) to dramatically increase the pressure of the volume of fuel and thereby to cause injection. Actuating fluid is ported to the intensifier by a valve controlled by a solenoid. The pressure of the incoming actuating fluid from the rail 42 controls the speed of the intensifier piston and plunger movement, and therefore, the rate of injection. The amount of fuel injected is determined by the duration of the pulse from the IDM 30 and how long it keeps the solenoid of the respective injector 60 energized. The intensifier amplifies the pressure of the actuating fluid and elevates the pressure of the fuel acted upon by the plunger from near ambient to about 20,000 psi for each injection event. As long as the solenoid is energized and the valve is off its seat, high pressure actuating fluid continues to push down the intensifier and plunger to continuously pressurize fuel for injection until the intensifier reaches the bottom of its bore.
Fuel economy is becoming more and more important. More efficiency in fuel usage is needed. The fuel consumption of the engine varies with engine speed and load. The need for actuating fluid also varies with engine speed and load, a higher volume of actuating fluid being required to develop sufficient high pressure fuel in the injector 60 at higher engine speeds and load. The actuating fluid pump 40 is engine driven and develops the same output at a given engine speed without regard for the volume of actuating fluid needed by the injectors 60. The volume is selected to ensure that the rail 42 is always fully charged with high pressure actuating fluid at the highest demand for actuating fluid. As noted above, excess actuating fluid is vented by the RPCV 50 to the reservoir 46. This means some engine power is used unnecessarily at lower to intermediate engine loads to run the actuating fluid pump 40. As noted above, in the prior art engines, the actuating fluid pump 40 is a one stage actuating fluid pump delivering actuating fluid to the pressurized rail 42. Under certain engine operating conditions, typically relatively low engine load, the unneeded actuating fluid is dumped to ambient (reservoir 46), resulting in energy loss.
In the prior art fuel injection system 10, pressurized actuating fluid (engine lubricating oil) is used to control the injected fuel quantity by using pressure amplification in the injectors 60. As noted above, a pressure source pumps actuating fluid to a pressure rail 42 (accumulator) where pressure is regulated according to the engine load and speed requirement. The pressure regulation is done via the pressure-regulating valve 50 that dumps excess pressurized actuating fluid to ambient in order to maintain the desired pressure in the rail 42. Although it is desirable to minimize the damped flow for efficiency purposes, the required demand must be maintained in order to assure stability of desired rail pressure.
In order to achieve a more efficient system, the delivery of the pump 40 must be controlled depending on the engine requirement. A continuous supply of actuating fluid to the rail is needed in order to maintain the desired rail pressure at any engine condition. Further, the engine power used to drive the actuating fluid pump should more nearly reflect the actuating fluid needed in the rail for the present engine operating condition.
The actuating fluid control system of the present invention is capable of meeting the aforementioned needs. By matching the power consumption of the actuating fluid pump to the engine needs, the engine fuel consumption is reduced, especially at lower engine load conditions. Further, a continuous supply of actuating fluid is supplied to the rail.
The pressure dynamics quality in the pressure rail 42 is a key player in such systems. The impact of transient flow discontinuity in the rail 42 has to be minimized. Dumping flow from a single actuating fluid pump as done in the past created objectionable high pressure fluctuations which were a significant source of transient flow discontinuity in the rail 42. Hence, a continuous steady flow from a pump stage to the rail 42 as provided for in the present invention has a stabilizing effect in the rail 42. Further, a proportional flow control valve as used in the present invention allows a smooth controllable pressure transition when transitioning from venting actuating fluid to supplying make up actuating fluid to the rail.
The multi-stage pumping system of the present invention, comprising a variable output pump, preferably two de-coupled pumps, is able to select the required flow rate according to the engine load and speed via a specific control strategy. This results in reducing the power used for driving the pump over the total range of engine operating conditions, power to the pump equaling fluid pressure times flow rate.
Depending on the engine need, by controlling actuating fluid pump delivery, the power lost in friction in the actuating fluid pump is ultimately reduced. A variable output or multi-stage actuating fluid pump system able to switch from one delivery quantity to another, according to the engine need, reduces the power consumption and, correspondingly, the fuel consumption. The switching strategy of the present invention is implemented via a three-way, two-position flow control valve connected to a low pressure pump. The flow control valve operates on and off to dump actuating fluid to ambient (no power consumption mode) or pump the actuating fluid to the rail (power consumption mode). The flow control valve is driven by a proportional solenoid. An injection pressure-regulating (IPR) valve, or RPCV, is incorporated for rail pressure regulation. A high-pressure pump is pumping actuating fluid continuously to the rail during engine operation, while a low-pressure actuating fluid pump is operated on and off, as noted above. The continuous flow from high-pressure pump is used to drive the system at loads ranging from zero to 50% load and acts to minimize rail pressure fluctuations while the low pressure pump is dumped to ambient.
The variable output or multi-stage pump of the present invention increases the overall efficiency of the engine by reducing the fuel consumption by 3 to 5%. The risk of noise and vibration due to pressure instabilities resulting from flow discontinuity and pressure spikes in the rail is reduced since the high flow pump pumps actuating fluid continuously during engine operation to insure stability of the system. Furthermore, a simple flow control strategy of the present invention can be implemented without major changes in the existing fuel system.
The present invention is a control system for controlling the flow of an actuating fluid to an accumulator, the accumulator serving the fuel injectors of an internal combustion engine, and includes a controller being in communication with a plurality of engine related sensors. A variable output pump is in fluid communication with a source of actuating fluid and has at least two selectable output conditions, the pump being operably coupled to the controller, the controller acting to selectively port a portion of the actuating fluid to the accumulator in a first pump output condition and to vent the portion of the actuating fluid to a reservoir in a second pump output condition. The present invention is further a fuel injection system and a method of control.